Optically anisotropic aromatic polyamide dopes

ABSTRACT

Compositions or dopes comprising carbocyclic aromatic polyamides in suitable liquid media are prepared which are optically anisotropic (exhibit different light transmission properties in different directions in the dope). These dopes, and related isotropic dopes, are used in preparing fibers of unique internal structure (evidenced by low orientation angle and/or high sonic velocity) and exceptionally high tensile properties (e.g., initial modulus).

United States Patent Kwolek 51 *June 20, 1972 [54] OPTICALLY ANISOTROPIC AROMATIC POLYAMIDE DOPES R f r n Cited [72] Inventor: Stephanie Louise Kwolek, Wilmington, UNITED STATES PATENTS D l. 6 3,063,966 11/1962 Kwolek et al. ..260/32.6 N [73] Assignee: E. 1. du Pont de Nemours and Company, 3,154,613 10/1964 Epstein et al..

Wflmmswn, Del. 3,232,910 2/1966 Preston ..260/32.6 N 1 Notice: The portion of the term f this patent 3,240,760 Prestonet 8i. N sequent to June 20 999 has b i 3,227,793 1/1966 Cipnam claimed. 3,414,645 12/1968 Morgan 260/30 2 3,472,819 10/1969 Stephens. 260/30 8 [22] Filed: May 23, 1969 [21] APPLNOJ 827,345 Primary E.\'aminerAllan Lieberman Attorney-Eugene Berman Related U.S. Application Data [63] Continuation-in-part of Ser. No. 736,410, June 12, [57] ABSTRACT 1968, abandoned, which is a continuation-in-part of Compositions or dopes comprising carbocyclic aromatic Ser. No. 644,851, June 9, 1967, abandoned, which is a polyarnides in suitable liquid media are prepared which are continuation-in-part of Ser. No. 556,934, June 13, optically anisotropic (exhibit different light transmission pro- 1966, abandoned. perties in difierent directions in the dope). These dopes, and related isotropic dopes, are used in preparing fibers of unique [52] US. Cl. ..260/30.8 R, 260/29.1 R, 260/302, 1 imema] structure id d b l i ntati angle and/ r 260/30 N high sonic velocity) and exceptionally high tensile properties [51] Int. Cl. ..C08g 51/44, C08g 51/46, C08g 51/50 (3%, initial modulus) [58] Field of Search ..260/30.2, 31.2 N, 30.8 R, 30.6 R,

ASOT/POP/ C 2 Claims, 9 Drawing Figures PATENTEDJUH20 I972 SHEET 10F 9 r. H K wk, 0 P 6 pm, n, m m mu w a+m p 3% M 5 AM mm z/fl O Nw m no 5 I I M MW p Z a 0 Z 5 P M a a w 6 H m m 8 6 4 a 4 /'c/ co/vc, 9. //00 ML 0M4 INVENTOR STEPHANIE LOUISE KWOLEK ATTORNEY PATENTEDJunao m2 SHEET '4 OF 9 ,q/v/so Wop/ LSO 7/?OP/C xoqz INVENTOR STEPHANIE LOUISE KWOLE K ATTORNEY PATENTEDJUH20 I972 SHEET 8 BF 9 INVENTOR STEPHANIE LOUlSE KWOLEK ATTORNEY P'A'T'ENTEflJunzo m2 SHEET 7 BF 9 am 3 x7 WW 2 5 W INVENTOR STEPHANIE LOUISE KWOLEK ATTORNEY PATENTEDJMO I972 SHEET 80F 9 INVENTOR $53: 5 m$= 225F252 mm 3 mm on we ow mm an 3 ON 2 2 s m Q 6 w e Q a 0 JV W o Q Q a o e x mm m x x a x x x a 5m: SEE E: x Q $5: ==lw w 6 x x x x x x A x xx x I x x x m* v x x i /\l.) E PS o o I!) com STEPHANIE LOUISE KWOLEK ATTORNEY OPTICALLY ANISOTROPIC AROMATIC POLYAMIDE DOPES CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of my copending application Ser. No. 736,410, filed June 12, 1968, now abandoned which in turn is a continuation-impart of my application Ser. No. 644,851, filed June 9, 1967, now abandoned which in turn is a continuation-in-part of my application Ser. No. 556,934, filed June 13, 1966, now abandoned.

This invention relates to novel, optically anisotropic dopes consisting essentially of carbocyclic aromatic polyamides in suitable liquid media. These dopes, and related isotropic dopes, are used to prepare useful fibers, films, fibrids, and coatings. In particular, fibers of unique internal structure and exceptionally high tensile properties are provided.

SUMMARY OF THE INVENTION The dopes of this invention which are optically anisotropic (as measured by procedures described hereinafter) comprise ingredients selected from the group of carbocyclic aromatic polyamides whose chain extending bonds from each aromatic nucleus are essentially coaxial or parallel and oppositely directed in suitable liquid media, exemplified hereinafter, which may contain additives. The amount of polymer in the dope exceeds the critical concentration point and preferably comprises at least about 5 percent by weight of the dope. These anisotropic dopes are structurally and functionally distinct from known polyamide solutions and are uniquely suited for the preparation of high strength shaped articles (e.g., fibers) often without post-shaping treatment (e.g., drawing).

The fibers of this invention are prepared from the above optically anisotropic dopes, or relates isotropic dopes, containing specified aromatic polyamides. These fibers are characterized by a unique internal structure and exceptionally high tensile properties, either as-extruded (as described hereinafter) or after being heat treated (as described hereinafter).

This unique internal structure of the fiber is evidenced by the fiber exhibiting a low orientation angle and/or high sonic velocity. Fibers of this invention exhibit orientation angles of less than about 45 and preferably less than about 35, most preferably less than about 25, measured as described hereinafter, and/or sonic velocity values of at least about 4 km./sec., preferably at least about 6 km./sec., most preferably at least about 7 km./sec., measured as described hereinafter.

The fiber possesses outstanding tensile properties, in particular, an initial modulus at least about 200 gpd. and preferably at least about 300 gpd., most preferably greater than about 400 gpd. and/or a tenacity at least about 5 gpd. Preferred as-extruded fiber of this invention exhibits an elongation of at least about 5 percent, in addition to high initial modulus and tenacity.

FIGURES The invention will be more fully explained with reference to the Figures wherein:

FIG. I illustrates a phase diagram of a poly(p-benzamide)/N,N-dimethylacetamide (containing water and lithium chloride) dope of this invention;

FIG. ll illustrates a typical relationship of viscosity and polymer concentration for the dopes of this invention, showing the critical concentration point;

FIG. III illustrates a typical trace of an X-ray difiraction pattern of poly(p-benzamide) homopolymer;

FIGS. IV and V further illustrate phase diagrams of dopes of this invention;

FIGS. VI and VII illustrate critical concentration points of particular dopesof this invention as a function of inherent viscosity; and

FIGS. VIII and IX illustrate the relationship ofthe fiber structural parameters, orientation angle, and sonic velocity,

respectively, to an important physical property (initial modulus) of the fiber.

DETAILED DESCRIPTION OF THE INVENTION Polyamides Among the suitable aromatic polyamides (of which the preferred anisotropic dopes of this invention are comprised and/or from which the fibers of this invention can be prepared) are those in which the chain extending bonds from each aromatic nucleus are essentially coaxial or parallel and oppositely directed. The term aromatic nucleus" is used herein to include individual enchained aromatic rings and fused-ring aromatic divalent radicals. The preferred polymers include carbocyclic aromatic polyamides containing up to 2 aromatic rings, including enchained non-fused rings (e.g.,4,4'- biphenylene) or fused rings (e.g., 1,5-naphthalene) per amide linkage. The chain-extending bonds from these aromatic rings are paraoriented and/or essentially coaxial or parallel and oppositely directed.

Highly preferred polyamides are characterized by recurring units of the formula:

( (I) 0 I! H wherein R and R (when the chain extending bonds are essentially coaxial) are selected from the group of:

% 4, 4-biphenylene and R and R (when the chain extending bonds are essentially parallel) are selected from the group of:

1, -phenylene, and

I 1, fi-naphthylene, and

2, fi-naphthylene R and R may be the same or different and may contain substituents on the aromatic nuclei.

Additional highly preferred polyamides of this invention are characterized by recurring units of the formula:

wherein R is selected from the group of:

QQ 4, 4-biphcnylene 1, 4-phenylene, and

substituents be present per aromatic nucleus. However, more than two such substituents may suitably be present if the substituent is a relatively small group, e.g., methyl.

Both homo-and copolyamides having substituted or unsubstituted aromatic nuclei, as described above, are well suited for the dopes and fibers of this invention. Random copolymers are preferred copolymers. By the term random" is meant that the copolymer consists of molecules containing large numbers of units comprised of two or more different types in irregular sequence. The units may be of AB (e.g., from paminobenzoyl chloride hydrochloride), AA (e.g., from pphenylenediamine or 2,6-dichloro p-phenylene diamine), or BB (e.g.,' from terephthaloyl or 4,4'-bibenzoyl chloride) type or mixtures of these, provided always that the requirements of stoichiometry for high polymer formation are met. It is not necessary that the relative numbers of the different types of the unit be the same in different molecules or even in different portions of a singlemolecule.

One or more of these polymers may suitably be used in the dopes and/or fibers of this invention, i.e., a single homopolymer; a single copolymer; or homopolymer and/or copolymer blends are suitable herein.

While the polymer chains described above consist essentially of amide links (COHN-) and aromatic ring nuclei as described above, the polymers useful for preparing the products of this invention may also comprise up to about percent (mole basis) of units not conforming to the abovecited description, e.g., aromatic polyamide-forming units whose chain extending bonds are other than coaxial or parallel and oppositely directed, e.g., they may be meta-oriented, or of linkages other than amide, e.g., urea or ester groups.

Among the suitable aromatic polyamides may be named poly(p-benzamide); poly(p-phenylene terephthalamide); poly(2-chloro-p-phenylene terephthalamide); poly(2,6- dichloro-p-phenylene 2,6-naphthalamide); poly(p-phenylene p,p'-biphenyldicarboxamide); poly(p,p-phenylene benzamide); poly(l,5-naphthylene terephthalamide); ordered aromatic copolyamides such as e. g., copoly(p,p'-diaminobenzanilide terephthalamide), and random copolyamides such as, e.g., copoly(p-benzamide/m-benzamide) (95/5); and many others.

It is to be understood that the designation of position locations of substituent groups on the aromatic nuclei of the polymers useful in this invention refers to the location(s) of the substituent(s) on the diamine, diacid, or other reactants from which the polymeris prepared. Thus e.g., random endto-end distribution of polymer-forming units in the chain, if possible, is comprehended by the name by which any given polymer is identified herein.

Polyamides, as described above, having an inherent viscosity (as described hereinafter) of at least about 0.7, and preferably greater than about 1.0, are fiber forming and particularly useful herein. Lower inherent viscosities may be utilized for films, fibrids and/or coatings.

POLYMER PREPARATIONS A preferred polyamide of this invention, substantially homopolymeric poly(p-benzamide), which consists essentially of recurring units of the formula:

(Ill) can be readily obtained by certain polymerization techniques from suitable monomers dissolved in particular solvents, which may contain lithium chloride and chain terminating agents if desired.

Suitable monomers include p-aminobenzoyl halide salts of the formula:

wherein Xfrepresents a member selected from the group consisting of arylsulfonate, alkylsulfonate, acid sulfonate, and halogen radicals, preferably bromide or chloride radicals, and X represents a halogen radical, preferably bromide or chloride. p-Aminobenzoyl chloride hydrochloride is the preferred monomer. Other monomers suitable are paminobenzoyl bromide hydrobromide, p-aminobenzoyl chloride hydrobromide, p-aminobenzoyl chloride methanesulfonate, p-aminobenzoyl chloride benzenesulfonate, paminobenzoyl chloride toluenesulfonate, p-aminobenzoyl bromide ethanesulfonate, and p-aminobenzoyl chloride acid sulfate. Other monomers, not within Formula (IV), e.g,, paminobenzoyl chloride sulfate, are also suitable. The preferred p-aminobenzoyl chloride hydrochloride may be prepared in high yield from an ethereal solution of pthionylaminobenzoyl chloride by the general procedure of Graf and Langer, J. prakt. Chem. 148, 161 (1937) under anhydrous conditions. The drying and anhydrous storage of this monomer are preferably performed under room temperature conditions because of the tendency of the compound to polymerize at higher temperatures.

Solvents which are suitable for the polymerization reaction include those selected from the group consisting of: N,N,N',N'-tetramethylurea, hexamethylphosphoramide, N,N-dimethylacetamide, N-methylpyrrolidone-Z, N-methylpiperidone-Z,

1 ,3-dimethylimidaZolidinone-Z, dimethylethyleneurea) N,N,N', N-tetramethylmalonamide, N-methylcaprolactam, N-acetylpyrrolidine, N,N-diethylacetamide, N-ethylpyrrolidone-Z, N,N-dimethylpropionamide, N,N-dimethylisobutyramide, N,N-dimethylbutyramide, and tetrahydro-l ,3-dimethyl-2( lH)-pyrimidinone dimethylpropyleneurea).

Salts, such as lithium chloride, are preferably added to the polymerization reaction mixture; such addition may assist in the maintenance of a fluid mixture.

Chain terminators, as indicated above, may be used in these polymerizations. By assisting in the control of the molecular weight of the polyamide, the use of chain terminators contributes to the ease by which subsequent processing of the polymer occurs and enhances the stability of the polymer dope for application in the hereinafter described coupled polymerization spinning process. Among the suitable chain terminators are monofunctional compounds which can react with the acid chloride ends of these polyamides such as ammonia, monoamines (e.g.,. methylamine, dimethylamine, ethylamine, butylamine, dibutylamine, cyclohexylamine, aniline, etc.), compounds containing a single amide-forming group, such as N,N-diethylethylenediamine, hydroxylic compounds such as methyl alcohol, ethyl alcohol, isopropyl alcohol, phenol, water, etc., and monofunctional compounds which can react with the amine ends of the polyamides such as other acid chlorides (e.g., acetyl chloride), acid anhydrides (e.g., acetic anhydride, phthalic anhydride, etc.), and isocyanates (e.g., phenyl isocyanate, m-tolyl isocyanate, ethyl isocyanate, etc.). Useful difunctional terminators include terephthaloyl chloride, isophthaloyl chloride, sebacyl chloride, 4,4-biphenyldisulfonyl chloride, pyromellitic dianhydride, p-phenylenediisocyanate, benzidine diisocyanate, bis(4-isocyanatophenyl)methane, p-phenylenediamine, mphenylencdiamine, benzidine, bis(4-aminophenyl) ether, N,N'-diaminopiperazine, adipic dihydrazide, terephthalic dihydrazide and isophthalic dihydrazide.

The polymerization reaction may be carried out by dissolving the desired monomer or monomers (as well as the chain terminating agent and lithium chloride, if any is used) in the desired amide or urea solvent and vigorously stirring the resulting solution, externally cooled, until it develops into a viscous solution or a thick gel-like mass. Alternatively, the desired monomer may first be slurried in a small quantity of an anhydrous, inert organic liquid, such as tetrahydrofuran, dioxane, benzene or acetonitrile, prior to the addition of the amide solvent. Preferably, the resulting monomer/organic liquid mixture is stirred at an increased rate and a relatively large volume of the amide solvent is rapidly added. In a further variation, the amide solvent may be frozen and mixed, while frozen, with the desired monomer. The solvent is permitted to thaw and the resulting mixture stirred until a viscous solution or gel-like mass forms.

In each of the above techniques, the polymerization reaction is maintained at low temperature, i.e., under 60 C. and preferably from -I 5 to +30 C., by external cooling, if necessary. The reaction mixture is stirred continuously until it gradually develops into a viscous solution or thick gel-like mass. The reaction is generally allowed to proceed a period of from about 1 to 48 hours, preferably from about 2 to 24 hours.

For the attainment of the highest molecular weights, these polymerizations are performed under strictly anhydrous conditions. The reaction vessel and auxiliary equipment, solvents, and reactants are carefully dried prior to use and the reaction vessel is continuously swept with a stream of dry, inert gas, e.g., nitrogen, during the polymerization.

The polymerization reaction produces an acidic by-product (e.g., HCl or HBr) which is preferably neutralized. Neutralization is especially preferred in embodiments hereinafter described wherein the reaction mixture is prepared for direct use in forming shaped articles of the polymer. In such a situation, it is preferred to add a base selected from the group consisting of:

lithium carbonate,

lithium oxide,

lithium hydroxide,

lithium hydroxide monohydrate,

lithium hydride,

calcium oxide,

calcium hydroxide calcium hydride, and

calcium carbonate. or mixtures thereof, to neutralize the reaction mixture. The use of a neutralization agent is highly desired, in that the acid may cause significant corrosion problems in processing equipment (e.g., the spinneret). Neutralization may also be necessary to achieve more fluid compositions which facilitate the formation of shaped articles. If more than the stoichiometric amount of neutralizing agent is used, an insoluble excess may remain. Its removal may be required prior to forming a shaped article (e.g., by spinning). The neutralizing agent may be added before, shortly after, or long after monomer is added to the reaction medium depending upon the inherent viscosity desired. Addition of neutralizing agent may result in a sharp increase in polymer molecular weight as determined by measuring the inherent viscosity of polymer isolated from an aliquot of the reaction mixture before and after neutralization.

In addition to excess neutralization agents, the dopes may contain other insoluble material which preferably should be removed, by conventional means, prior to forming a shaped article. For example, when the acidic polymerization system produces bromide ion and lithium hydroxide is used as a neutralizing agent, the lithium bromide produced may be insoluble in particular dopes and should be removed before the dope is spun or cast.

The composition or dope may be concentrated under vacuum to produce a fluid of the desired solids content and/or viscosity for spinning or casting, under the conditions discussed hereinafter.

To isolate the poly(p-benzamide), the polymerization mixture is combined with a polymer nonsolvent, e.g., water in a suitable blender, and thereby is converted to a powder. The powdered polymer, after being washed with both water and alcohol, is dried overnight in a vacuum oven at about 60 C. before being stored or treated for subsequent processing.

The essentially homopolymeric poly(p-benzamide), prepared as previously described, possesses a peak height ratio (PI-IR) of below 0.86 and, moreover, no sediment is seen in the tube when the polymer is subjected to a sedimentation test, all as described hereinafter. It will be understood, however, that the peak height ratio as measured on a sample of this polymer that has been spun or heated at elevated temperatures may exceed 0.86; the sedimentation properties of such a sample may also be different. Poly(p-benzamide) having a PHR greater than 0.86 is also useful in this invention, e.g., anisotropic dopes of this polymer in HF or oleum.

Other polyamides useful in this invention may be prepared from appropriate coreactants by low temperature solution polymerization procedures (i.e., under 60 C. and preferably from 10 to 30 C.) similar to those shown in Kwolek et al. U.S. Pat. No. 3,063,966 for preparing poly(p-phenylene terephthalamide). For example, such polyamides may be prepared by causing p-phenylenediamine or 2-chloro-p-phenylenediamine to react with polyamide-forming derivatives of terephthalic acid. This dicarboxcylic acid is conveniently employed in the form of its dihalides which are readily prepared by well-known methods; the diacid chloride is usually preferred. Preferably, these low temperature solution polymerizations are accomplished by first preparing a cooled solution of the diamine in a solvent or a mixture of solvents selected from the group of hexamethylphosphoramide, N- methylpyrrolidone-Z, and N,N-dimethylacetamide. To this solution is added the diacid chloride, usually with stirring and cooling. Polymer precipitation frequently occurs within a few minutes and on other occasions the reaction mixture may gel. It may be desirable in some cases to stir or permit the reaction mixture to stand for 30 minutes to several hours or more. The polymer may be isolated by agitating the reaction mixture with a polymer non-solvent, e.g., water, in a suitable blender. The polymer is collected, washed, and dried before being stored or subsequently processed into a dope.

Illustrations of preparations of other useful polymers and copolymers are shown in the examples which follow. These preparations may also include in situ synthesis of directly extrudable anisotropic dopes (e. g., see Example 4 herein).

DOPE PREPARATION Polymers and copolymers which have been prepared by the previously described methods and which have been isolated after formation, may be combined with a suitable liquid medium (including additives, if any, e.g., LiCl) to form compositions or dopes (such embodiments will hereinafter be referred to as isolated polymer dopes). In certain other embodiments, the polymerization medium is utilized to form such compositions or dopes (such embodiments will hereinafter be referred to as in situ polymer dopes) in a coupled" polymerization spinning process.

Liquid media useful for forming the anisotropic dopes of this invention, as well as related isotropic dopes, include:

1. Selected amides and ureas, including: N,N- dimethylacetamide, N,N-dimethylpropionamide, N,N- dimethylbutyramide, N,N-dimethylisobutyramide, N,N- dimethylmethoxyacetamide, N,N-diethylacetamide, N-

methylpyrrolidone-2, N-methylpiperidone-2, N-methylcaprolactam, N-ethylpyrrolidone-2, N-acetylpyrrolidone, N-acetylpiperidine, N,N'-dimethylethyleneurea, N,N'-dimethylpropyleneurea, hexamethylphosphoramide and N,N,N,N- tetramethylurea, which may contain lithium chloride and/or calcium chloride.

2. Concentrated sulfuric acid whose concentration is greater than about 90 percent by weight, usually 98-100 percent by weight H 80 or oleum (i.e., concentrated sulfuric acid containing up to 20 percent or higher of free S which may contain additives (e.g., Nal-IPO Na,SO potassium acetate which may be present in the amount of 2-3 percent by weight of the total dope). The selection of the sulfuric acid concentration most suited for a particular dope preparation is based upon, in part, the inherent viscosity of the polymer employed.

3. l-lydrofluoric acid, used alone or in combination with additives such as water (1-2 percent by weight, of the total dope), NaF or KF 1-2 percent by weight of the total dope), an inert chlorinatedhydrocarbon (e.g., CH Cl or mixtures thereof (in an amount up to 5 percent by weight of the total dope).

4. Chloro-, fluoroor methane-sulfonic acids used alone or in combination with additives such as lithium chloride (up to about 2.5 percent by weight).

Mixtures of two or more of the above liquid media may be used in suitable combinations e.g., any of the amides and ureas; hydrofluoric acid and fluoro-sulfonic acid; methane sulfonie acid and sulfuric acid; oleum and chloro-, fluoroor methane-sulfonic acid; and the like.

The use of additives, as described above, is preferred in many of the dopes of this invention. It is believed that particular additives aid the solvation of the polyamide in the liquid medium. For the amide and urea media, it is highly desirable that at least about 2.0 weight percent of lithium chloride and/or calcium chloride be added to provide a reasonably concentrated dope from particular isolated polymers, e.g., poly( 1,4-benzamide). In the preparation of amide or urea in situ dopes, the salt may be added before, during or after the polymerization, preferably by forming it as a byproduct of a neutralization (e.g., when the monomer is p-aminobenzoyl chloride hydrochloride and the neutralization agent is lithium carbonate, a by-product of the neutralization reaction is lithiurn chloride). In the preparation of an amide or urea dope from isolated polymer, the salt may be conveniently added to the polymer and/or liquid medium. In either type of dope (isolated or in situ) salt in excess of about weight percent is generally neither necessary nor desired, less than about 15 weight percent is preferred, about 4 to 8 weight percent being most preferred. For liquid media, other than amides and ureas, the use of other solvation additives (e.g., as indicated above) may also be desirable; generally small amounts (e.g., less than about 5 weight percent) of these additives are used.

Although the dopes consist essentially of the polymer and the liquid medium (including additive, if any), additional substances may be present in the dope, such as small amounts of inert organic liquids (e.g., tetrahydrofuran, dioxane, benzene, or acetonitrile) .used to disperse the monomer in the amide or urea dopes, water (either purposefully added or adventitiously present) and the acidic by-product of the polymerization reaction (e.g., if less than the stoichiometric amount of a neutralization agent is used).

The usual additives such as dyes, fillers, delusterants, UV stabilizers, antioxidants, etc., can be incorporated with the polymer or copolymer or dispersed in the dopes of this invention for the purposes intended, prior to the preparation of shaped articles thereof.

Dopes of this invention may be conveniently prepared e.g., by combining polymer and the liquid medium (and additives, if any) in a conventional manner (e.g., with stirring). Some dopes are formed at room temperature conditions and are useful (e.g., spinnable) under these conditions. Other dopes require specific heating techniques, i.e., flowable compositions may be obtained at room temperature in many instances,

while heating, preferably with stirring, and sometimes heating and cooling cycles are required in a few instances. The amount of heating and/or cooling required to form a useful dope or composition varies with the liquid medium, the polymer (the composition, the inherent viscosity, the crystallinity, and the particle size of the polymer sample employed) and the quality of the stirring action. In the preparation of these dopes, care must be taken to avoid local overheating and formation of a dry" or gelled spot at the meniscus of this composition or on the walls of the vessel being employed. Such portions of polymer frequently do not readily redissolve. Numerous suitable techniques useful in preparing specific dopes of this invention are illustrated in the Examples.

The anisotropic dopes of the invention may comprise a single anisotropic phase, or an emulsion of anisotropic and isotropic phases in any proportion or degree of dispersion. The isotropic dopes also useful in preparing fibers of this invention comprise a single isotropic phase. Minute quantities of undissolved polymer may be present in these phases or in the emulsion, particularly when the dope is prepared by dissolving isolated polymer. A dope" is a shaped-structure-forming (e.g., fiber-forming, film-forming, or fibrid-forming) polymersolvent system which comprises at least one of the above phases.

Anisotropic Dopes When the dope-forming ingredients of this invention are combined in particular concentration ranges, the resultant dopes are optically anisotropic, i.e., microscopic regions of a given dope are birefringent; a bulk dope sample depolarizes plane-polarized light (described hereinafter), sometimes referred to herein as light or polarized light, because the light transmission properties of the microscopic areas of the dope vary with direction. This characteristic is associated with the existence of at least part of the dope in the liquid crystalline or mesomorphic state. As described in Industrial Research, G. H. Brown, May, 1966, pp. 53-57, liquid crystals are intermediate between the liquid and solid states in many of their properties. Thus, they have unique structural arrangements partially imparting the order of crystals and the fluidity of liquids.

The dopes of this invention exhibit anisotropy while in the relaxed state. Although conventional polyamide dopes may depolarize plane-polarized light when subjected to appreciable shear (e.g., flow birefringence wherein molecules in a solution are hydrodynamically oriented), static (i.e., stationary) samples of the dopes of this invention uniquely exhibit this phenomenon.

The extended stiff-chain aromatic polymers which are present in the anisotropic dopes of this invention are believed to be in essentially rod-like entities (aggregates or bundles) in the liquid medium. This extended, stiff-chain configuration of the polymer is indicated by values of the exponent, a, in the Mark-Houwink relationship, [1;]=KM ,for dilute solutions of lower molecular weight polymer. In this well-known relationship, [n] is the intrinsic viscosity, M is the molecular weight, and K and a are constants for a given polymer/solvent system. The great majority of polymers for which this relationship has been evaluated in the literature have had values below 0.9. Among the polymers used in the dopes of this invention, poly(p-benzamide) is determined to have an a value of 1.6, measured on unfractionated polymer with an inherent viscosity in the range of 0.4 to 2 and weight average molecular weight determinations made in sulfuric acid (-98 percent by weight). When a given system exceeds a certain critical concentration point, an anisotropic phase is formed which gives rise to the characteristics of the anisotropic dopes of this invention.

For a given polyamide/liquid medium dope of this invention, below a particular polyamide concentration, the dope is isotropic. As the concentration of the polyamide increases, the viscosity of the dope increases. However, at a point referred to herein as the critical concentration point" there is a sharp discontinuity in the slope of the viscosity vs. concentration curve when the dope changes from isotropic to partially anisotropic without the fonnation of a solid phase. Further addition of polyamide results in a decrease in the viscosity of the dope, as the dopes become more anisotropic. An exemplary viscosity vs. concentration curve is described in Example 73 and illustrated in FIG. II.

As previously stated, a given dope of this invention is anisotropic when the ingredients of the dope are present in particular concentration ranges. There is a complex relationship existing among the concentration of the polymer or copolymer, the inherent viscosity thereof, and the temperature which generally determines the ranges in which a given polymer or copolymer/liquid medium dope is anisotropic. Exemplary phase relationships are shown in Example 64 and FIG. I, and Example 74 and FIGS. IV and V. Such relationships for other dopes of this invention can be easily determined by routine experimentation.

The critical concentration point varies with the particular polyamide, as well as the weight percent and the inherent viscosity thereof, the particular liquid medium and the temperature. The effect of the weight percent of polymer and temperature on dopes of two different polyamides is shown in Example 75. The effect of the inherent viscosity on two different polyamides is shown in Example 74 and FIGS. VI and VII.

Anisotropic dopes comprising polymers and copolymers, as previously described, incorporating up to about 10 percent (mole basis) of aromatic units whose chain extending bonds are not essentially coaxial or parallel and oppositely directed may be prepared according to this invention. For example, random high molecular weight copoly(p-benzamide/mbenazmide) (95/5) may be prepared from p-aminobenzoyl chloride hydrochloride and m-aminobenzoyl chloride hydrochloride by the previously described low temperature solution polymerization techniques. A dope prepared from such a copolyamide in, e.g., N,N-dimethylacetamide and lithium chloride, exhibits optical anisotropy.

Anisotropic dopes of aromatic copolyamides wherein all chain-extending bonds from each aromatic nucleus are essentially coaxial or parallel and oppositely directed are also comprehended by the present invention. For example, an ordered copolyamide prepared from 4,4'-diaminobenzanilide and terephthaloyl chloride or 2,6-naphthaloyl chloride may be incorporated into an anisotropic dope comprising the (l) copolymer, an amide mixture, and lithium chloride, or (2) the copolymer, a suitable sulfuric acid or oleum.

One spinnable group of anisotropic dopes comprises about 6-15 percent by weight poly(p-phenylene terephthalamide) whose inherent viscosity is in the range of about 0.7-3.5, from 0.5 percent to up to 5 percent by weight lithium chloride, and the balance an. amide mixture of hexamethylphosphoramide and N-methylpyrrolidone-2 containing greater than 45 percent by volume of hexamethylphosphoramide. The relative amounts of these ingredients, particularly those of the hexamethylphosphoramide and N-methylpyrrolidone-2, contribute to the ease with which these spin dopes are obtained. For instance, as illustrated in the examples which follow, a spin dope fluid at room temperature is obtained from these ingredients when a particular amide mixture is employed. However, when a different amide mixture containing more hexamethylphosphoramide is employed with the same amounts of the polymer and salt, the combined ingredients must be heated to at least about 35 C. to achieve a liquid anisotropic dope whose birefringence may be observed. Preparation of the dopes is preferably undertaken by vigorous mixing of the ingredients at low temperatures, e.g., as low as to -l0 C.

Another spinnable group of anisotropic dope comprises about -25 percent by weight poly(2-chlorop-phenylene terephthalamide) whose inherent viscosity is in the range of about 0.7-3, from 0.5 percent to up to 8 percent by weight of lithium chloride and the balance being N,N-dimethylacetamide. In addition, anisotropic dopes comprising (1) poly(2- chloro-p-phenylene terephthalamide), lithium chloride, and N,N,N',N'-tetramethylurea (TMU) and (2) the same polymer with N,N-dimethylacetamide and calcium chloride can be prepared. For example, an anisotropic dope is prepared by combining 2.5 g. of poly(2-chloro-p-phenylene terephthalamide) (ninh 1.27) with 25 ml. of a mixture prepared from 3.56 g. of lithium chloride and ml. of TMU. This dope produces a bright field in a polarizing microscope and displays transmittance value (T) of 81 as measured herein.

There is a complex relationship existing among the amount of poly(2-chloro-p-phenylene terephthalamide) and the inherent viscosity thereof, the amount of salt, and the amount(s) of amide(s) that determine whether or not a given dope preparation is optically anisotropic under otherwise constant conditions. By way of illustration, an isotropic dope may be converted to an anisotropic dope by changing the polymer concentration. For example, a clear dope comprising 10 g. of poly(2-chloro-p-phenylene terephthalamide), ninh 1.13, in 100 ml. of a mixture of 100 ml. of N,N-dimethylacetamide and 4.3 g. of lithium chloride is isotropic. However, when an additional 10 g. of the polymer is added thereto, the resulting dope becomes turbid and anisotropic as shown by light depolarization studies. That the amount of salt present in the dope contributes to the nature of the dope is demonstrated by observing that a dope comprising 20 g. of poly(2-chloro-p-phenylene terephthalamide), 'ninh 1.13, and 100 ml. of a mixture of 100 ml. of N,N-dimethylacetamide and 7 g. of lithium chloride is isotropic.

Dopes comprising poly( 2-chloro-p-phenylene terephthalamide) can be separated into 2 layers, an isotropic upper layer and a more dense anisotropic lower layer. This separation can be achieved by, e.g., permitting a spin dope to stand for a period of time sufficient to achieve the separation (e.g., one week) or by, e.g., centrifugation. Just as an isotropic poly(2- chloro-p-phenylene terephthalamide) dope can be converted to an anisotropic dope by changing polymer concentration at constant polymer inherent viscosity, a change in the volume of a given anisotropic phase in a two-layer dope system can be attained by incorporating in the dope a polymer of higher inherent viscosity. For example, a dope comprising 10 g. of poly(2-chloro-p-phenylene terephthalamide), 'r inh 1.13, in 100 m1. of a mixture obtained by combining 100 ml. of N,N- dimethylacetamide and 3.12 g. of lithium chloride separates into 2 layers on long standing. The bottom layer is 20 percent of the total volume. When the dope is prepared with 10 g. of this polymer with an inherent viscosity of l .85, the anisotropic bottom layer constitutes 33 percent of the total volume. It has been observed that the maximum amount of salt which may be present in an anisotropic dope of this polymer increases as the inherent viscosity of the polymer employed to prepare the dope increases.

It is to be understood that the combinations of the aforesaid ingredients are chosen to provide an anisotropic dope; certain combinations of ingredients may not so provide. For example, poly(p-phenylene p,p'-biphenyldicarboxamide) and poly(p,p'-phenylene benzamide) which form anisotropic dopes in oleum, do not form anisotropic dopes in HF or in some of the amides and ureas useful with other polymers of this invention. Whether a given dope is anisotropic is readily determined by the methods described hereinafter.

DETERMINATION OF OPTICAL ANISOTROPY In the examples which follow, the anistropic character of the dopes of this invention is described in terms of e.g., 1) by plotting the relationship of dope viscosity vs. polymer concentration to determine the critical concentration point, (2) by numerical values of transmittance of light through crossed polarizers, identified as T" or DDA," (3) an observation of the bright field observed in a polarizing microscope, and (4) a visual determination o stir opalescence."

Critical Concentration Point A critical concentration point" characterizes the anisotropic dopes of this invention, i.e., there is a sharp discontinuity in the slope of the dope viscosity v. polymer concentration curve. When the concentration exceeds this point, the dope is anisotropic and further addition of polymer results in a decrease in the viscosity as the dope becomes more anisotropic. This point" (as well as the complete viscosity v. concentration curve) is routinely determined using conventional concentration and viscosity measuring techniques. For example, a polymerdope of this invention may be placed in a polyallomer test tube equipped with a Teflon TFBfluorocarbon cap through which a viscometer spindle extends into the dope, constant temperature being maintained. The viscosity of the stirred dope may be conventionally measured with a viscometer (e.g., a Brookfield Syncho-Lectric Viscometer,

Model RV, product of the Brookfield Engineering Laboratories, lnc., Staughton, Mass, or equivalent). Viscosity measurements are made at the initial polymer concentration and at higher concentrations (i.e., after an additional known amount of polymer is added). By this technique (or equivalent) a viscosity vs. concentration curve may be plotted for this system (the given polymer and liquid medium at that temperature) and the critical concentration point (i.e., the discontinuity in the slope of the curve) is determined.

T Test The determination of the T" value may be made by placing an anisotropic dope of this invention, prepared as described herein and containing no suspended solid matter, between a crossed polarizer and an analyzer. The dope sample is conveniently employed as a layer 80 p, thick. Thus, a drop taken from the interior ofa dope sample of this invention is put on a dry, clean strain-free glass slide; a square cover of glass, supported on one edge by a glass tube or wire of known thickness 1.3 mm. diameter is convenient), is pressed down on the drop so as to form the roof of a liquid wedge. The edges are sealed with a fast-drying binder (e.g., Duco cement. DuPonts registered trademark for a transparent, flexible, waterproof adhesive avoiding actual contact with the dope. The sharp edge of the wedge is sealed by excess dope which is squeezed out. In the operation, common care should be taken to avoid evaporation, moisture uptake, excessive shearing actions, dirt, and any suspended solid particles.

The samples are allowed to stand for a sufficient time to permit relaxation of the shear stresses resulting from the slide preparation to assure that the sample is static. For example, the amide or urea dopes are relaxed about l minutes; up to about 1 k hours is generally needed to relax sulfuric acid dopes (especially the more viscous samples); up to about 1 hour is generally sufficient to relax the other dopes of this invention, e.g. fluoro and chloro-sulfonic acid dopes.

The wedge is positioned in a light beam, on a microscope stage between crossed polarizer and analyzer. The light beam has the intensity such as is ordinarily used in microscopic examinations. The wedge is positioned so that the thickness of the center of the layer of dope through which the light beam passes is 80 p. in thickness. The intensity is measured with polarizer and analyzer crossedik flsuperscript s to denote sample present in wedge) and with analyzer removed(l )and the difference I l+ is obtained. The transmitted light may be measured by conventional light sensitive detectorstegby photo multipliers, selenium or cadmium light meters, bolometers, etc.). The same measurements are then made on a similarly constructed wedge containing air, and the difference -'-l- (superscript c for control) is recorded. When the dopes of this invention are placed in the wedge the expression (lJ-LQ-(lJ-L will be greater than zero and greater than can be accounted for by experimental error. using reasonable care and accurate instrumentation. It represents the increase in light transmittance through the analyzer due to the presence of the sample. The magnitude of (L -L (lJ-L') will vary with the solvent being used, polymer concentration. concentration of dissolved salt. and the units in which light intensity is measured.

in the examples, an apparatus by which the anisotropic character, or T value, of the dopes is determined consists essentially of an A. 0. Spencer Orthoscope llluminator which contains a tungsten overvoltage microscope lamp (color temperature 3,800 K.), an optical wedge containing the sample, an optical wedge containing air, a Bausch and Lomb Polarizing Microscope having a Leitz 10X objective and a Leitz 10X ocular Periplan, a Gossen Sinarsix" exposure meter and a Polaroid MP3 Industrial Land Camera body. The wedge containing the sample is prepared as previously described and is positioned on the microscope stage (i.e., between the polarizer and the analyzer) to provide a sample layer 1. thick in the path of any light which reaches the analyzer and the light meter. The polarizer and the analyzer are adjusted to provide crossed polarization planes. Light from the lamp which passes the analyzer by the route previously described is projected into the camera body and is measured in the image plane (at the ground glass level) by the exposure meter L). The same measurement is made with the analyzer removed (l3). This is repeated with the control wedge of air 80 p. thick to give L and L. The light values from the Sinarsix exposure meter, which are expressed in logarithmic units to the base 2, may be converted to logarithmic units to the base 10 by multiplying them by 0.30l (i.e., by log 2): the antilogsm of these products are then determined. These antilog values are designated L if. if, and l Comparative intensity measurements, free from the particular intensity units, are conveniently stated in terms of relative intensities (i.e.. intensity ratios or fractions of transmitted light intensities). The expression l-"/l is the fraction of light intensities transmitted by the dope being examined. The fraction l.'/ l." is the fraction of light transmitted by the control wedge. The difference (l."'/L")(l-"/lf') represents the increase in intensity of light transmitted due to the presence in the wedg e ofthe dope being examined.

Since for a depolarizing sample, the theoretical maximum vale of l-"/l-" l-"/l 0.5, an index of the increase of light transmittance (T) may be conveniently taken as Z(l."/ l "lf/l since in this way the maximum value is 100. When measured according to the foregoing procedures; dopes having values greater than 4 are considered herein to be anisotropic in nature.

in which the primes denote measurements on a blank (completely isotropic), e is an opacity factor in the sense that two thicknesses of a given absorber have an e value twice as great as a single thickness, and 1r and 0 denote measurements made with polarizer and analyzer parallel and perpendicular, respectively. This is essentially a percent-difference equation. In practice, the incident light intensity is always adjusted so that a measurement of and (1 corresponding to unity (i.e., a 100 percent transmission'reading) is obtained with parallel polars for both (i blank and (2) sample, indicating for (l) a total lack of depolarization and for (2) a complete depolarization for the field observed. In this case the DDA equation is simplified to The scale is from zero to 100, with the former indicating perfect isotropy and the latter perfect anisotropy for the field observed.

The apparatus used for making DDA measurements consists of a Bausch and Lomb polarizing microscope (polarizer rotatable, analyzer fixed). The light source is a Silge and Kuhne Orthollluminator B with a lOO w G E. BMY bulb operated at a constant 115v. The light intensity to regulate e, (and e',,) is changed by the neutral filters and in's diaphragm in the illuminator. A light sensitive resistor, 0.15. 8-1036,

. sating), to photoresistor.

All measurements are made in red light produced by a red band pass filter (with a transmission region from about 600m to a maximum of about 650mg. in the visible range) in the illuminator. The photoresistor is calibrated with a series of Kodak Color Compensating filter films, CCSOR; an opacity of l 100 percent transmission on meter) being assigned to a single film, 2 to two films, etc. During calibration the films are placed on the microscope stage and the microscope focused approximately at the center of the stack of filter films (vertically). The operating conditions imposed on the photoresistor are designed to produce a linear calibration curve with log meter reading plotted against opacity. Sample opacities are then taken directly from the calibration curve. This gives a relative red-opacity" value for the sample.

Samples are prepared for measurement by extracting a drop of dope from the interior of the bulk sample. This is placed on a .Pyrex" glass disk. An annular Teflon fluorocarbon spacer, 0.002 in. (51p) thick is placed on the disk and a second glass disk closes the cell. This assembly is placed into a spacial screw-assembly which seats the glass against the spacer assuring a constant 0.002 in. sample thickness (with the sample substantially filling the cell). These samples are allowed to relax for l-l.5 hours before measurements are made. Blanks are prepared in the same way with pure solvent.

In making visual observations (crossed polarizers in microscope) on the dopes for which DDA is measured, any positive value for DDA indicates the presence of some anisotropic phase. The higher the DDA, the greater the amount of anisotropic phase present in the dope except in the extreme limits with less than about 5 percent of one phase present. This is due partly to the sensitivity of the apparatus. Also when the proportion of anisotropic phase is low and not uniformly distributed or dispersed, small fields of view can be selected which have less than average or even no anisotropic phase. A 100 percent anisotropic dope does not always give a DDA 100, probably because of irregularities in the texture. Observation Between Light Polarizing Elements The T and DDA tests described above, quantitively describe the light transmittance of anisotropic dopes. However, a qualitative determination can also be conveniently made using a light source, analyzer and crossed polarizer (or equivalents thereof) as described in these tests. When such polarizing elements are crossed, a static (relaxed) dope sample placed between the polarizer and analyzer will transmit es- 5 sentially no light if the dope is isotropic. However, when the sample is anisotropic, light will be transmitted and a relatively bright field will be observed (the intensity of the light being related to the degree of anisotropy of the sample). A more detailed description of the type of field observed in dopes containing anisotropic and/or isotropic phases is set forth in Ex ample 64. Stir Opalescence Stir opalescense" is a term used herein to describe a property characteristic of anisotropic dopes which is visually observed with the naked eye. Many of the dopes of this invention, when observed in bulk in a transparent vessel, appear turbid or hazy and yet they contain no, or practically no, undissolved solid. When the dope, seen under reflected ordinary light, is disturbed by tilting or rolling of the vessel or by only slow stirring, there is produced a characteristic, readily-observed, satin-like sheen or glow which is observed even after the disturbance ceases and which decreases in intensity thereafter. With some compositions there is produced no sense of color while others may have a bluish tone or even a degree of varigated color, which is described by observers as having a pearly or opalescent quality. Extraneous color in the dope, such as yellows from minor impurities or inherent in some polymers, modifies the observation of color developed under shear. Dopes, which are disturbed as described above, often give the appearance of having striations and/or graininess in the surface. These visual effects are observed in anisotropic dopes of this invention. While such effects do not conclusively establish that the dope is anisotropic, such dopes generally are anisotropic or will become anisotropic upon the addition of more polymer (providing solubility limits permit). For the sake of brevity, the visual observation of all variations of the phenomenon outlined above is referred to in the examples as the exhibition of stir opalescense.

Dopes described as anisotropic hereinafter may have shown this stir opalescense effect or may have been shown to be anisotropic by the aforementioned qualitative or quantitative techniques, i.e., the critical concentration point is determined or the sample is observed between light polarizing elements, as in a microscope, to depolarize plane-polarized light, either qualitatively or quantitatively, as described hereinbefore. Any of the above-described qualitative or quantitative techniques suitably indicate anisotropy, although one or more of such techniques may be more convenient and/or accurate for a given dope. The determination of critical concentration point is the preferred test for determining anisotropy because it is conveniently and accurately used for all anisotropic dopes of this invention. The qualitative test (visual observation between light polarizing elements) is preferred for the convenience in testing a large number of samples. The stir opalescence observation is also convenient and generally indicates anisotropy. Among the quantitative tests (other than the critical concentration point determination), the DDA test is preferred for sulfuric acid dopes because it is more sensitive in borderline anisotropic measurements in such dopes; the T test is generally preferred for amide or urea dopes. Although the T and DDA tests are generally suitable for all dopes of this invention, since hydrofluoric acid (in HF dopes or generated by the fluoro-sulfonic acid in other dopes) attacks glass, care and/or altered testing procedures may be necessary, (e.g., substituting a strain-free, HF -resistant slide for the glass slide and shielding the microscope lens from HF gas).

UTILITY OF THE DOPES FIBER PREPARATION The previously described compositions or dopes of this invention can readily be utilized for the production of fibers, films, fibrids, and coatings.

Dopes of this invention containing at least 5 percent by weight of polymer are preferred in that they are particularly useful in preparing fibers. Although these anisotropic dopes are useful in preparing other shaped articles, the preferred use of these dopes (as well as related isotropic dopes) is in the preparation of fibers by conventional techniques and/or techniques described herein. The term fibers is used generically herein to include the numerous conventional fiber structures. For example, the fibers may be of staple or continuous lengths. similarly, the fiber may consist of a single component or multicomponents (e.g., a bicomponent fiber with the two components consisting of different polyamide compositions of this invention). Furthermore, one or more polyamide compositions of this invention may be in a given fiber (or fiber component) i.e., the fiber may contain a single polyamide composition or blends of two or more of such compositions. The fibers may be employed in single strands or multi-fiber bundles (e.g., yarns). All such conventional fiber structures which consist essentially of the polyamide compositions specified herein, having the internal structure and properties specified herein, are contemplated herein.

The compositions or dopes of this invention are extruded into fibers by conventional wetand dry-spinning techniques and equipment. In wet spinning, an appropriately prepared composition containing the polymer and, e.g., an amide or urea medium, whose temperature may vary from to about 100 C., is extruded into a suitable coagulating bath, e.g., a water bath maintained at 090 C., depending on the solvent used in the preparation of the dope. Other useful coagulants include ethylene glycol, glycerol, mixtures of water, methanol and an amide or urea solvent, mixtures of water and alcohols and aqueous salt baths, e.g., maintained at a temperature of about 20 to +90 C. Dry spinning may be accomplished by extruding the compositions or dopes of this invention, into a heated current of gas whereby evaporation occurs and filaments of the polyamide are formed.

After being formed, the fibers may be passed over a finishapplication roll and wound up on bobbins. Development of maximum levels of fiber and yarn properties may be assisted by soaking the bobbins in water or in mixtures of water and water-miscible inert organic liquids, (e.g., acetone, ethyl alcohol, glycerol, N,N,N',N'-tetramethylurea, N,N- dimethylacetamide) to remove residual amide liquid and salt or acidic solvents followed by drying. Removal of the residual solvents and/or salts may also be accomplished by passing the fiber or yarn through aqueous baths on the run, by flushing the bobbins with water as yarn is formed, and by washing or soaking skeins, rather than bobbins, of yarn. Dry-spun yarn may be strengthened by washing with even a minor amount of water.

The fibers prepared from the anisotropic compositions or dopes of this invention and related isotropic dopes, are characterized by a unique internal structure and exceptionally high tensile properties, either as extruded or after being heat treated.

This unique internal structure of the fiber is evidenced by its low orientation angle and/or high sonic velocity. The physical meaning or orientation angle is that it establishes an angle (i.e., one half of the orientation angle) about the fiber axis in which a given percentage of crystallites are aligned. In the fiber of the present invention, a high percentage (i.e., greater than about 50 percent, generally about 77 percent) of the crystallites are aligned within this angle (one half of the orientation angle) about the fiber axis; this percentage is determined from an intensity trace of the fibers diffraction pattern (as described hereinafter). For example, the intensity trace is an essentially Gaussian curve for most of the fibers of this invention (i.e., essentially all of the heat-treated fibers and most of the as-extruded fibers). For such a curve, about 77 percent of the diffraction intensity falls within this angle and this is interpreted as showing that a like percentage of crystallites is aligned within this angle. For the few fibers (e.g., some of the as-extruded fibers) for which the curve may not be Gaussianlike (e.g., the curve may be a composite of several curves exhibiting partially resolved peaks), greater than about 50 percent of the crystallites are aligned within this angle, (see Example 83).

In addition to the orientation angle characterization, fibers of this invention are characterized by sonic velocity. Sonic velocity is a structural parameter relating to the fibers molecular orientation along the fiber axis. A higher value of sonic velocity is the result of a higher degree of molecular orientation along the fiber axis. Sonic velocity and related parameters are described by Charch and Moseley in the Textile Research Journal, Vol. XXIX, No. 7, 525-535 (1959) and by Moseley in the Journal of Applied Polymer Science," Vol. III, No. 9, 266276 1960).

Orientation angle and/or sonic velocity demonstrate the unique internal structure of the fiber. These structural parameters each relate to orientation and each evidence the uniqueness thereof. Sonic velocity is a measure of the total molecular orientation as contrasted with crystalline orientation. This total molecular orientation differs from the orientation described by orientation angle, i.e., orientation angle is a measure of crystallite orientation determined by X-ray measurements. The unique internal structure of the fibers of this invention is evidenced by either or both of these orientation parameters; each parameter suitably describes the uniqueness and the parameters are correlated for the fibers of this invention.

The unique internal structure of the fibers of this invention is believed to be responsible for the exceptionally high tensile properties thereof. The relationship between the fiber structural parameters (orientation angle and sonic velocity) and the fibers tensile properties is illustrated in FIGS. VIII and IX. These figures, prepared from data given in the following examples, show that for fibers of this invention as the orientation angle decreases (FIG. VIII) and/or the sonic velocity increases (FIG. IX), the initial modulus increases.

In general, as shown in the examples which follow, fibers of this invention possess these high tensile properties as-spun" or as-extruded. As-spun" or as-extruded" fibers of this invention are defined asthose formed in the normal processes of spinning (i.e., forming, shaping, or finishing steps), but which are not submitted to a drawing (elongation) or heattreating operation which changes the molecular order or arrangement of polymer molecules. However, the fibers may be subjected to washing and drying operations needed to remove solvents or impurities. Other operations which may be carried out without changing the fundamental character of the fibers include (1) application of finishes, dyes, coatings, or adhesives; (2) physically treating the fiber by twisting, crimping, cutting into staple; (3) using the fiber in forming snaped objects, fabrics, papers, resin or rubber composites; etc.

As-extruded fibers of this invention are preferred for par ticular end uses e.g., tire cord. For such uses, it is generally desirable that, in addition to high modulus and tenacity value, the fiber exhibits elongation of at about 5 percent. However, post-shaping treatments (e.g., heat treatment) which improve the modulus and tenacity, often do reduce the elongation (e.g., to below 5 percent). Since particular preferred fibers of this invention possess desirably high moduli and tenacities asextruded, and exhibit elongation values of at least about 5 percent, these as-extruded fibers are well suited for such end uses.

The as-extruded tensile properties of both the wetand dryspun as-extruded fibers can be enhanced by subjecting the undrawn fibers to a heat treatment. Hot air ovens, hot pins, hot slots, hot plates, liquid heating baths are useful for such treatments. The tensile properties of the as-extruded fibers are preferably enhanced by heating the fiber, maintained in a taut state, or drawn in a nitrogen atmosphere maintained at a temperature in the range of about 300l ,OO0C., preferably 500-600 C., for from 0.1 second to 5 minutes, preferably 0.1-l0 seconds as subsequently shown.

The fibers of this invention possess excellent chemical and thermal properties. They retain their tensile properties after being heated and boiled for 0.5 hr. in aqueous hydrochloric acid (1 percent) and caustic (1 percent) solutions. The fibers are essentially unaffected after being soaked for 1 hr. at 60 C. in commercially used dry cleaning solvents such as perchloroethylene and trichloroethylene. The fibers are selfextinguishing when they are removed from an open flame.

The excellent tensile properties of the fibers of this invention make them especially useful as reinforcing agent for plastics, tire cord, V-belts, etc.

The compositions or dopes of this invention may be formed into films by a conventional wet-extrusion method; such films are usually kept under restraint when they are subsequently dried and washed. Compositions prepared in the abovedescribed manner also may be formed into fibrids by shearprecipitation techniques (e.g., as described in Morgan U.S. Pat. No. 2,999,788), or applied as a liquid coating to a variety of substrates which may be in the form of sheets, papers, wires, screens, fibers, fabrics, foams, solid or microporous objects, etc. The substrates may be glass, ceramics, brick, concrete, metal (e.g., copper, steel, aluminum, brass), wood and other cellulosic materials, wool, polyamides, polyesters, polyacrylonitrile, polyolefins, polyvinylhalides, cured epoxy resins, cured aldehydeurea resins, etc.

Generally, an anisotropic dope can be used to produce an as-extruded fiber of properties superior to those of fibers MEASUREMENTS AND TESTS Inherent Viscosity: the following equation:

Inherent viscosity (ninh) is defined by ln rel) wherein ('qrel) represents the relative viscosity and (C) represents a concentration of 0.5 gram of the polymer in 100 ml. of solvent. The relative viscosity ('nrel) is determined by dividing the flow time in a capillary viscometer of a dilute solution of the polymer by the flow time for the pure solvent. The dilute solutions used herein for determining (nrel) are of the concentration expressed by (C), above; flow times are determined at 30 C., using concentrated (95-98 percent) sulfuric acid as a solvent, unless otherwise specified.

Fiber Tensile Properties: Fiber properties of tenacity, elongation, and initial modulus are coded as T/E/Mi and are reported in their conventional units, i.e., grams per denier, percent, and grams per denier. Denier is coded as Den. Such properties are conveniently measured in accordance with ASTM operational specifications, D76-53, (Oct. 1962), utilizing a testing machine, e.g., an lnstron tester (product of the lnstron Engineering Corp., Canton, Mass), providing a constant rate of extension. Unless otherwise specified, samples having a break elongation of up to about 8 percent are tested at a rate of extension of %/minute; samples of higher break elongation are tested at 60%lminute. Samples are filaments which measure 1 inch (2.54 cm.) in length or yarns having 3 turns/inchwhich measure 10 inches .4cm.) in length; and testing is done at 21 C. and 65% R.H.

Samples are not boiled off (scoured) but generally are conditioned at 21 C. and 65% RH. for at least 16 hours (sometimes expressed herein as as is), unless otherwise specified. If boil-off is specified, it consists of boiling the filaments or yarns for minutes in 0.1 percent aqueous sodium lauryl sulfate, rinsing, drying at C. for 1 hr. and conditioning at 21 C. and 65% R.l-l. for at least 16 hours, unless otherwise specified.

Fiber Heat Treatment: Unless otherwise stated in the examples, the post-extrusion heat treatment process applied to the fibers and yarns obtained from fluid compositions and dopes of this invention comprises washing or soaking the asextruded fiber or yarn in water until essentially free of the spinning media and/or salt, drying them, then heating them in one of the devices described below.

Device A The device consists of an inner stainless steel tube 32 in. (81.3 cm.) X 0.3125 in. (7.94 mm.) (I.D.) mounted concentrically in a second tube [1.06 in. (2.69 cm.) O.D.], the whole assembly being centered in a 12 in. (30.48 cm.) electric furnace. Nitrogen gas enters through 2 nipples in the outer tube located 10 in. (25.4 em.) out from either side of the center of the tube, such that the incoming nitrogen passes through the annular space between the two tubes. The nitrogen passes from the annular space into the inner tube through a small hole located in the wall of the inner tube to its center and thence out the ends of the inner tube at such a rate as to change the atmosphere in the 12 in. (30.48 cm.) heated zone of the inner tube at least once a minute. The outer ends of the device which protrude from the furnace are wrapped with asbestos fiber and glass tape to within about 2 in. (5.08 cm.) of each end. The temperature of the furnace is controlled by a thermocouple brazed to the center of the outside wall of the outer tube and connected to Minneapolis-Honeywell Pyrovane controller. The heated tube has a temperature ninh profile with the maximum temperature in the center region. The nominal heat-treating temperature is determined by a thermocouple brazed to the outer central surface of the inner tube. In passing fibers through the tube, guides are used to keep the fiber centered and out of contact with the tube walls. Device 13 This is identical with Device A, above, in terms of tube dimensions, furnace type, etc., and is operated in the same general manner. This device differs from A, above, in the amount of insulation wound on the ends and in the fact that the nitrogen inlets are on opposite sides of the outer tube in Device A but are on the same side in Device 13. Differences in nitrogen flow rates may exist between the two devices. Device C The device consists of an inner stainless steel tube 35 in. (89 cm.) X 0.5 in. (1.27 cm.) (I.D.) mounted concentrically in a second tube [i.e., a l in. (2.54 cm.) diameter stainless steel pipe, 18 in. (45.7 cm.) long], the whole assembly being centered in a l2-in. (30.48 cm.) electric furnace. Nitrogen gas enters through two nipples attached to the ends of the outer tube (one at each end of the outer tube) such that the incoming nitrogen passes through the annular space between the two tubes. The nitrogen passes from the annular space into the inner tube through two small holes located in the wall of the inner tube at its center and thence out the ends of the inner tube at such a rate as to change the atmosphere in the 12 in. (30.48 cm.) heated zone of the inner tube at least once a minute. The outer ends of the device which protrude from the furnace are wrapped with glass wool to within about 2 in. (5.08 cm.) of each end. The temperature of the furnace is controlled by a Minneapolis-Honeywell Pyrovane controller, by means of a thermocouple in contact with the center of the outside surface of the inside tube. The heated tubehas a temperature profile with the maximum temperature in the center region. The nominal heat-treating temperature is determined by a second thermocouple in contact with the outer central surface of the inner tube. In passing fibers through the tube, guides are used to keep the fiber centered and out of contact with the tube walls. Device D The device consists of a stainless steel tube, 0.286 inch (7.26 mm.) inside diameter and 32 inches (81.3 cm.) in length. The tube has a hot nitrogen stream piped into its center and out through its ends at a rate which changes the atmosphere inside the tube once per minute. The tube is mounted in a concentric steel pipe through which the nitrogen passes prior to entering the yam-treating zone. The entire assembly is mounted inside a small l2-inch (0.3 m.) long, combustion furnace. A thermocouple is brazed to the external surface of the steel pipe and is positioned close to the furnace elements. The output of the thermocouple is connected to a Minneapolis-I-loneywell Pyrovane controller, which controls the temperature of the furnace and pipe at such a level that a thermocouple brazed to the outside surface of the inner heat treating tube at its center indicates the temperature at that region. Additional heaters are wrapped around the portion of the heat-treating tube which protrudes from the combustion furnace. A typical profile of the temperature in the tube (for a center or nominal" temperature of 536 C.), obtained by varying the position of a test thermocouple, is given below:

TEMPERATURE PROFILE OF HEAT-TREATING TUBE When appropriate in the examples which follow, the use of Device A, B, C and D in treating fibers is indicated, together with the nominal heat-treating temperature observed for the central section (approximately 1-2 inches) of the inner tube for that device.

Peak Height Ratio: A measure of the relative intensity of the two major equatorial diffraction peaks for poly(p-benzamide) is given by the peak height ratio (Pl-1R). A suitable method for determining the PHR involves the use of a reflection technique to record the intensity trace of the X-ray diffraction pattern with an X-ray difiractometer.

The measurement is made using poly(p-benzamide) isolated as follows. The polymerization mixture is combined slowly with a large excess of polymer non-solvent, e.g., water, vigorously stirred in a suitable blender, and thereby converted to a powder or finely granular form. The powdered polymer is thoroughly washed with water, and optionally with ethanol, by repeated stirring in the blender followed by filtration, and is dried in a vacuum oven at 6090 C. before being stored or treated for subsequent processing.

Approximately 0.5 gram of waterand amide-or urea-free polymer is pressed into a sample holder under an applied pressure of 3,125 lb./in. (219.8 X g./cm. Using CuKa radiation, a trace of the intensity is recorded from 6 to 40, 26, and with 0.5 slits, at a scanning speed of 1, 26, per minute, a chart speed of 1 inch (2.54 cm.) per minute, and a time constant of 2; 26 is the angle between the undifiracted beam and the diffracted beam. The full scale deflection of the recorder is set so that the peak with maximum intensity is at least 50 percent of the scale, which is a linear scale. To calculate the PHR, a base line is first established on the diffractometer scan by drawing a straight line between the points on the curve at 8 and 38, 26. Vertical lines (at constant 26 values) are drawn from the peaks in the vicinity of 20.3 and 23.4, 26, to the base line, and the height of the peaks, in chart divisions, above the base line is ascertained. The PHR is then calculated from the equation PHR A/B where A=height of the peak, approximately located at 20.3,

26, above the base line in chart divisions, B=height of the peak, approximately located at 23.4", 26, above the base line in chart divisions.

A typical trace of an X-ray diffraction pattern of powdered poly( 1,4-benzamide) homopolymer isolated from preparations in amide or urea media appears in FIG. III. A smooth line was drawn as indicated to compensate for instrument noise and the measurements are made therefrom.

Sedimentation Test: To a solution of 1.0 g. of dry lithium chloride in 30 ml. of dry N,N-dimethylacetamide is added 0.5 g. of dry polymer powder and comminuted to a particle size of about p. or less. The tube is stoppered and its contents, heated at 60-80 C., are subjected to stirring by a mechanical agitator for a period of from 10 min. to 45 hrs. 1f polymer particles remain visible, the contents of the tube are cooled to 70 C. (e.g., by immersion in a bath of solid carbon dioxide and acetone), then are allowed to warm up until stirring can be resumed, and are heated as above. The tube is then allowed to stand upright for a further 24 hours without stirring. After this time, if no polymer residue lies settled on the bottom of the tube, the sample is said to satisfy the Sedimentation Test.

Crystallinity: The degree of crystallinity indicated by the X-ray diffraction patterns is assessed in a qualitative manner by visual examination and use of the following terms:

amorphous: having only diffuse rings or arcs,

trace: much diffuse scatter with some sharpening of the principal spots,

low: moderate degree of sharpness in the spots with appreciable surrounding diffuse scatter,

medium: quite sharp spots but with the retention of some diffuse character,

high: very sharp diffraction spots and essential absence of diffuse scattering. With increasing crystallinity, the number of diffraction spots usually increases.

It is to be understood that these ratings are only intended as a differentiation of the range of crystallinities observed for species of fibers within this invention and not as a limitation thereof.

Orientation Angle: The orientation angle of the fiber (filament) is determined by the general method described in Krimm and Tobolsky, Textile Research Journal, Vol. 21, pp. 805-22 (1951). A wide angle X-ray difiraction pattern (transmission pattern) of the fiber is made using a Warhus pin-hole camera. The camera consists of a collimator tube 3 in. (7.6 cm.) long with two lead (Pb) pin-holes 25 mils (0.0635 cm.) in diameter at each end, with a sample-to-film distance of 5 cm.; a vacuum is created in the camera during the exposure. The radiation is generated by Philips X-ray unit (Catalog No. 12045) with a copper fine-focus diffraction tube (Catalog No. 32172) and a nickel beta-filter; the unit is operated at 40 kv. and 16 ma. A fiber-sample holder 20 mils (0.051 cm) thick is filled with the sample; all the filaments that are in the X-ray beam are kept parallel. The diffraction pattern is recorded on Kodak No-Screen medical X-ray film (NS-54T) or equivalent. The film is exposed for a sufficient time to obtain a pattern which is considered acceptable by conventional standards (e.g., a pattern in which the difiraction spot to be measured has a sufficient photographic density, e.g., between 0.2 and 1.0, to be accurately readable). Generally, an exposure time of about 45 minutes is suitable; however, a lesser exposure time may be suitable, and even desirable, for highly crystalline and oriented samples to obtain a more accurately readable pattern. The exposed film is processed at a temperature of 68% 2 F. in Du Pont Cronex X-ray developer for 3 min., in a stop bath (30 ml. of glacial acetic acid in 1 gal. [3.785 1.] of distilled water) for 15 sec., and in General Electric Supermix X-ray fixer and hardener solution for 10 min. The film is washed in running water for 0.5 hr. and is dried.

The arc length in degrees at the half-maximum intensity (angle subtending points of 50 percent of maximum intensity) of the principal equatorial spot is measured and taken as the orientation angle of the sample. The specific arcs used for orientation angle determinations on fibers described in the following examples (in the order presented in the following section) occurred at the following positions, 26 (degrees):

Fiber of Example 26 (Degrees) 1(Al) 22.56 1(H-1) 22.41 1(A-2) 22.56 1(H-2) 22.51 2 (A) 22.49 4(A) 24.35 4(1-1) 15.59 6(A) 22.73 7(A) 22.44 7(H) 21.45 8 (A) 22.10 8 (H) 22.19 9 (A) 21.20 9 (H) 22.00 10(A) 22.32 10(H) 21.82 11 (A) 21.55

11 (H) 21.78 13 (A) 22.39 13 (H) 22.22 14(A) 22.34 14 (H) 22.12 15 (A) 22.44 15 (H) 22.46 16(A) 22.44 16(H) 22.32 17 (A) 22.93 17 (H) 22.59 18 (A) 22.51 18 (H) 22.15 19 (A) 22.68 19 (H) 22.29 20 (A) 22.17 20(H) 22.15 21 (A) 21.60 

2. Dope of claim 1 wherein said liquid medium is concentrated (greater than about 98 percent by weight) sulfuric acid which may contain free SO3. 